Ceramic materials are used in various electronic parts such as semi-conductor IC packages, transistor headers, etc. They require good electrical insulation characteristic and reasonable mechanical strength and thermal conductivity.
Conventionally, alumina (Al.sub.2 O.sub.3) is used as a dielectric material for microelectronic packages. It has excellent electrical (insulating) and mechanical (especially strength), and thermal properties.
In some applications of the ceramic material, it is further required that it should also have a high degree of heat emissivity so that a large amount of heat may not be stored in the ceramic body, and that the ceramic body should be opaque so that no light is transmitted therethrough. To meet the requirements, it is common practice to color the ceramic body to black or near-black, i.e. purple, by adding suitable metals and/or metal oxides as coloring agents.
U.S. Pat. No. 3,791,833 issued to Sugiura et al discloses a ceramic composition for use in electronic equipment comprising at least one of Al.sub.2 O.sub.3 and BeO as a basic component, 0.1 to 5 percent by weight CoO and a further additive chosen from the group consisting of MnO.sub.2, Cr.sub.2 O.sub.3, V.sub.2 O.sub.5, Fe.sub.2 O.sub.3 and mixtures thereof.
U.S. Pat. No. 4,818,731 issued to Mizutani et al discloses a colored frit and method for manufacturing of artificial stone. The colored frit is prepared by heating a material composition comprising a devitrifying substance, a coloring agent and glass. The devitrifying substance is fluoride in an amount of 0.5 to 20 wt.%.
U.S. Pat. No. 4,481,261 issued to Johnson et al discloses blister-resistant dielectric material for use with multilayer circuits. The dielectric is comprised of 10-25% of an oxide mixture of Cr.sub.2 O.sub.3, Co.sub.2 O.sub.3 and Fe.sub.2 O.sub.3 which has been heated to about 1000.degree. C. and it prevents the blistering.
U.S. Pat. No. 4,769,294 issued to Barringer et al discloses alumina material for low temperature cosintering with refractory metallization. Colorants such as MnO, MoO.sub.3 or TiO.sub.2 or a combination thereof are added in amounts up to approximately 2% by weight to opacify the fired ceramic.
Japanese Patents 63,182,252, and 63,182,253 disclose a black ceramic alumina body. The colorant used to obtain the black color includes MoO.sub.2 and Cr.sub.2 O.sub.3.
Japanese Patent 53,137,216 disclose a colored ceramic alumina body. The colorant used to obtain the reddish violet color includes Cr.sub.2 O.sub.3 and metallic molybdedum and/or tungsten in an amount equal to or less than the chromium. The material is sintered in a nonoxidizing atmosphere.
The use of colorant has several serious drawbacks in the formation of alumina components. The first is that the cost of the colorants is relatively large as compared to the cost of the alumina body. It would be advantageous, therefore, to devise a method of coloring an alumina body to match a specified color and intensity using the least amount of costly colorants.
Colorants effect the properties of the fired alumina body. When colorants are added in an amount exceeding a predetermined maximum value, the electrical, mechanical and thermal characteristics inherent in alumina are deteriorated beyond the point of utility for a given application. The development of multilayer ceramic circuit boards for higher frequency, higher density and higher speed devices tends to decrease the maximum amount of colorants that can be added to the alumina body. At the same time if the amount of colorants does not reach a critical minimum level, the resulting color of the fired body will not match a specified color and intensity.
Accordingly, the primary object of the invention is to provide a colored ceramic body for use in various electronic parts, which has excellent electrical, mechanical and thermal characteristics, and in which the volume resistivity is not deteriorated when the ceramic body has been treated in a reducing atmosphere.
Another object of the invention is to obtain a purple colored alumina body using the least amount of coloring metals and metal oxides to obtain the desired intensity.
These and other objects and advantages of the present invention will be more fully understood and appreciated with reference to the following description.